(1) Field of the Invention
The present invention relates to a content receiving apparatus which receives contents, and in particular, to a technology for controlling a validity period of a key used in encrypting a content requiring copyright protection.
(2) Description of the Related Art
Recently, with the enhancement of communication infrastructures and the development of network technologies, images and music expressed in digital data (hereinafter referred to as “contents”) are exchanged actively on networks. For example, there is a case where a content recorded by a DVD recorder is viewed from a TV via a network or is dubbed in another DVD recorder via a network.
Dubbing does not need a real-time capability, so it can be suspended if other processing of higher priority cuts in. For instance, when a TV program for which recording has been scheduled on a DVD recorder is about to start, dubbing is suspended so as to start recording the TV program, and the dubbing is resumed after the recording ends. This enables the system as a whole to efficiently perform processing.
As a method for suspending and resuming transmission of a content via a network, a method in which Hyper Text Transfer Protocol (HTTP) is used for transmitting a content, and the range of the content is specified in the range header is being considered (e.g. refer to “Hypertext Transfer Protocol-HTTP/1.1”, by R. Fielding et al., RFC2616). That is, when a transmission of a content is resumed, the content receiving apparatus specifies, in the range header, a range where transmission has not been completed, and transmits a GET request using HTTP to a content transmitting apparatus. In this manner, there is no need to transmit the content again from the beginning, and thus efficient suspension and resumption can be realized.
Note that for premium contents requiring copyright protection such as contents transmitted in recent digital terrestrial broadcasting, there are cases where dubbing is not allowed, and only moving is allowed. When a premium content is moved, the premium content on the content transmitting apparatus side is deleted or made unusable (e.g. refer to Digital Transmission Content Protection Specification Volume 1 (Informational Version), Hitachi, Ltd, Intel Corporation, Matsushita Electric Industrial Co., Ltd., Sony Corporation, Toshiba Corporation, Revision 1.4, Feb. 28, 2005). However, a premium content must not be deleted from the content transmitting apparatus when it has not been stored correctly on the content receiving apparatus. For example, Japanese Laid-Open Patent Application No. 2002-366440 discloses a method for conveying, to a content transmitting apparatus, that a premium content has been received correctly by the content receiving apparatus. Further, Japanese Laid-Open Patent Application Nos. 2004-5816 and 2001-84177 disclose methods for restoring an original premium content on a content transmitting apparatus side when the premium content is not stored correctly in the content receiving apparatus due to some reason.